I believe there are different 'weights' of Rally mousse, depending on what weight of bike you are riding - like you suggest, a fully-fulled 75bhp 690RR is going to put a lot more strain on the tyres than a 50bhp CRF450 for example...

And I know there are are different rated front Desert mousses too - Patsy tends to specify the stronger/stiffer version for front wheels (to help minimise dented rims), and of course you'd want to run a Desert specific mousse in a Desert tyre, not a regular MX/enduro mousse (which will be softer, and smaller)...

Jx

true, I knew there were different flex mousse's, I had all my spares for the 525 and threw a set on the 640 for arse'ing around at home